1. Field of the Invention
The present invention relates to a scroll type compressor, and a method for preparing it, the compressor having the inside of a hermetic housing divided into a high pressure space and a low pressure space, and having a crankshaft supported in a way to sandwich an electric motor portion between both ends of the crankshaft.
2. Discussion of Background
In FIG. 14, there is shown a longitudinal sectional view of a conventional scroll type compressor. In FIG. 15, there is shown a longitudinal sectional view of parts shrinkage fitted in the compressor of FIG. 14. Reference numeral 1 designates a fixed scroll which has a base plate 1a provided with a scroll wrap 1b thereon. Reference numeral 2 designates an orbiting scroll which has a base plate 2a provided with a scroll wrap 2b thereon. The scroll wraps 1b and 2b are reverse to each other in the direction in which the scroll wraps are wound, and are combined to form a compression chamber 4. Reference numeral 3 designates a discharge port which is formed in the base plate 1a to communicate with the compression chamber 4. Reference numeral 7 designates a frame which is formed with a flange 7b. The base plate 1a is fixedly supported on the upper end surface of the flange. The flange 7b has an outer peripheral surface formed with a stepped portion 7c. The flange 7b has an inner peripheral surface formed with a concentric assemblage jig mounting surface 7d, the concentric assemblage jig mounting surface being concentric with a bearing 13 which is located at a central portion of the frame 7. Reference numeral 6 designates a crankshaft which has an intermediate portion provided with an electric motor rotor 8, and which is rotatably supported by the bearing 13. Reference numeral 23 designates a center shell which has an intermediate portion provided with a glass terminal 42, and which supports an electric motor stator 9 on an inner peripheral surface. The center shell has an upper inner peripheral surface formed with a stepped portion 23a, which is engaged with the stepped portion 7c. To the center shell 23 is fixed the frame 7 at an upper end side of the stepped portions 7c and 23a by shrinkage fit. Reference numeral 27 designates a subframe which is fixed to an inner peripheral surface of a lower end of the center shell 23 by welding, and which has a central portion formed with a bearing 39 for supporting the crankshaft 9 at its lower end. The bearing 39 has a lower portion formed with a concentric assemblage jig mounting surface 27b concentric therewith, a pumping element 43 being housed on the concentric assemblage jig mounting surface 27b. Reference numeral 20 designates a discharge chamber which is mounted to the upper end of the center shell 23 to close it. Reference numeral 40 designates a low pressure space which is formed under the frame 7. Reference numeral 41 designates a high pressure space which formed in the discharge chamber 20. The center shell 23 have the lower end closed by a lower shell 10, and an oil stored therein.
In operation, the crankshaft 6 which is driven by an electric motor comprising the electric motor stator 9 and the electric rotor 8 rotates while being supported by the bearings 13 and 39. The base plate 2a of the orbiting scroll 2 is eccentrically connected to the upper end of the crankshaft 6, and is supported on the frame 7 so as to be capable of carrying out orbiting movement. The rotation of the crankshaft 6 gives orbiting movement to the orbiting scroll 2 to form the compression chamber 4 between the fixed scroll 1 and the orbiting scroll 2. A low pressure refrigerant gas which has been introduced into the low pressure space 40 from outside is inspired into the compression chamber 4 by the action of compression between both scrolls 1 and 2, and is compressed into a high pressure refrigerant gas. The high pressure refrigerant gas is discharged from the discharge port 3 into the high pressure space 41, and leaves outside though a discharge pipe 5 which is mounted to the discharge chamber 20. As shown in FIG. 15, the stepped portion 7c in the frame 7 is supported by the stepped portion 23a in the center shell 23. Thrust which is caused on the frame 7 due to a difference between the pressure in the low pressure space 40 and that in the high pressure space 41 is received by the center shell 23. Such arrangement can prevent the frame 7 from axially shifting in the center shell 23. The outer peripheral surface of the flange 7b and the inner peripheral surface of the center shell 23 are fixed together at the upper end side of the stepped portions 7c and 23a by shrinkage fit to hermetically separate the high pressure space 41 and the low pressure space 40.
In order to assemble the frame 7 and the subframe 27, it is required that misalignment and inclination of the bearing 39 of the subframe 27 with respect to the bearing 13 of the frame 7 fall in predetermined precision ranges. Now, a method for assembling the frame 7 and the subframe 27 will be explained, referring to FIGS. 16 and 17. In FIG. 16, the frame 7 and the electric motor stator 9 have been previously fixed to the center shell 23 by shrinkage fit, and the electric motor rotor 8 is inserted in the center shell 23 in such a state that the end of the center shell 23 adjacent to the frame 7 faces downward. The center shell 23 with the frame 7 and the electric motor stator 9 fixed thereto and the electric motor rotor 8 inserted thereinto is placed on a table 45a to put the concentric assemblage jig mounting surface 7d of the frame 7 into engagement with a concentric assemblage jig 44a, and to position a fixed scroll mounting surface 7e of the frame 7 on a top surface of the table 45a. On the other hand, the subframe 27 is mounted onto a bottom surface of a table 45b to put the concentric assemblage jig mounting surface 27b of the subframe 27 into engagement with a concentric assemblage jig 44b, thereby positioning a reference surface 27c of the subframe 27 onto the bottom surface of the table 45b. The table 45b and the concentric assemblage jig 44b are vertically slided from such conditions to insert the subframe 27 into the center shell 23 until the subframe 27 is set at a predetermined height as shown in FIG. 17. During this process, the subframe 27 should not get in touch with the inner peripheral surface of the center shell 23. Finally, the subframe 27 is fixed to the center shell 23 by means of arc spot welding. In order that the misalignment and the inclination of the bearing 39 with respect to the bearing 13 fall in the predetermined precision ranges, coaxiality of the concentric assemblage jig mounting surface 7d with respect to the bearing 13, perpendicularity of the fixed scroll mounting surface 7e with respect to the bearing 13, coaxiality of the concentric assemblage jig mounting surface 27b with respect to the bearing 39, perpendicularity of the reference surface 27c with respect to the bearing 39, coaxiality of the concentric assemblage jig 44b with respect to the concentric assemblage jig 44a, and parallelism of the table 45b with respect to the table 45a are required to fall in predetermined precision ranges as a prerequisite. In addition, the arc spot welding should have no effect on a relative position or posture of the subframe 27 with respect to the frame 7.
The structure of the conventional scroll type compressor, which has been described in detail, does not ensure coaxiality between an outer peripheral surface of the subframe 27 and the inner peripheral surface of the center shell 23. In order to prevent the subframe 27 from getting in touch with the center shell 23 during inserting the subframe 27 into the center shell 23, a remarkable great clearance is required between the subframe 27 and the center shell 23. The sizes of the clearance significantly vary, depending on the positions of the arc spot welding. As a result, when the subframe 27 is fixed to the center shell 23, there are variations in strain due to arc spot welding, depending on the positions of the arc spot welding. This creates a problem in that the relative position and the posture of the bearing 39 with respect to the bearing 13 are changed, and the misalignment and the inclination go out of the predetermined precision ranges, lowering a fabrication yield.
It is a first object of the present invention to solve this problem, and to provide a scroll type compressor capable of realizing a high yield without being adversely affected by a change in a relative position and a posture of a subframe bearing with respect to a frame bearing due to arc spot welding, and a method for preparing such a scroll type compressor.
By the way, there has been known a scroll type compressor wherein a bearing which supports one end of the main shaft for driving an orbiting scroll is supported by a subframe, and the subframe is fixed to a side wall of a hermetic shell by means of spot welding.
Referring now to FIG. 18, there is shown a cross sectional view showing the structure of such a conventional scroll type compressor.
In FIG. 18, reference numeral 101 designates a fixed scroll which is constituted by a base plate 101a and a spiral wrap 101b projecting from it. Reference numeral 102 designates an orbiting scroll which comprises a base plate 102a and a spiral wrap 102b projecting from it. Reference numeral 103 designates a frame which has one side provided with a flange 103a, and which has the other side provided with a bearing 103c. The flange 103a has the fixed plate 101a fixedly supported at a top end surface, and the flange 103a defines a recessed portion 103b at a central portion, where the orbiting scroll 102 is put to carry out an orbital movement. The bearing 103c is formed to project in the axial direction for supporting one end of a main shaft, which is described later on.
Reference numeral 104 designates a hermetic shell which is constituted by a center shell 104a and dish-shaped end shells 104b, the center shell 104a being formed in a cylindrical shape and having the flange 103a fixed to an upper inner peripheral surface thereon by means of shrinkage fit, and the dish-shaped end shells 104b being fixed to the center shell 104 by welding the end shells to both ends of the center shell 104 at their circumferences in a continuous sequence to close the open ends of the center shell. Reference numeral 105 designates a compression chamber which is defined between both spiral wraps 101b and 102b. Reference numeral 106 designates a high pressure space which is formed between the base plate 101a and the end shell 104b. Reference numeral 107 designates a discharge port which is formed through a central portion of the base plate 101a to communicate between the compression chamber 105 and the high pressure space 106.
Reference numeral 108 designates a subframe which has a central portion provided with a bearing 108a to companion to the bearing 103c of the frame 103, and which has an outer side surface provided with a plurality of radial ribs 108b, as shown in FIG. 19 depicting the section taken along the live 19--19 of FIG. 18. Each rib 108b has an outer side surface fixed to a lower inner peripheral wall of the center shell 104a by means of spot welding. Reference numeral 109 designates the main shaft which has the one end supported by the bearing 103c of the frame 103 and the other end supported by the bearing 108a of the subframe 108, and which is rotatably connected to the orbiting scroll 102 at the one end side. In a central portion of the main shaft, a bore 109a is formed therethrough so that a lubricating oil which is supplied through a pumping device 110 arranged in the subframe 108 flows through the bore 109a.
Reference numeral 111 designates a low pressure space which is defined under the frame 103. Reference numeral 112 designates an electric motor which is arranged in the low pressure space 111 to rotate the main shaft 109, and which is constituted by an electric motor rotor fixed to the main shaft 109 by e.g. press fit, and an electric motor stator fixed to an inner side wall surface of the center shell 104a. Reference numeral 113 designates a glass terminal which is mounted in a side wall of the center shell 104a to feed power to the electric motor 112.
Now, how to fix the subframe 108 and the end shell 104b to the center shell 104 by welding will be described in more detail. As shown in FIG. 19, firstly, the outer side surfaces of the respective ribs 108b of the subframe 108 are inserted to a predetermined position along the inner peripheral wall of the center shell 104a, and the ribs 108b are fixed to the center shell 104a by arc spot welding. Welding points by the arc spot welding are indicated by reference numerals 114a, 114b and 114c. When the subframe 108 is fixed, the precision of the respective parts is controlled so that the subframe 108 is coaxial with the frame 103 on the order of a few .mu.m-a few tens .mu.m.
Next, the end shell 104b is press fitted into the center shell 104a in a light manner, and then a single welding torch is usually used to seal the end shell 104b to the center shell 104a around its circumference by continuous arc welding while moving the torch or rotating the center shell 104a and the end shell 104b. The starting point of the arc welding is indicated by reference numeral 115a.
The conventional scroll type compressor which is constructed as stated above carries out the following operations as generally well known. The main shaft 109 which is driven by the electric motor 112 rotates, being supported by the bearing 103c of the frame 103 and the bearing 108a of the subframe 108, thereby causing the orbiting scroll 102 to carry out an orbital movement. Such an orbital movement allows a low pressure refrigerant gas in the low pressure space 111 to be inspired into the compression chamber 105 defined by the wraps 101b and 102b of the fixed scroll 101 and the orbiting scroll 102. After the refrigerant gas is compressed in the compression chamber 105 to become a high pressure refrigerant gas, it is discharged into the high pressure space 106 through the discharge port 107, and leaves outside the hermetic shell 104.
Since the conventional scroll type compressor is constituted as stated earlier, when the end shell 104b is connected to the center shell 104a by arc welding, the point where a melted metal starts solidifing is located near to the welding starting point 115a. As a result, the end shell 104b is drawn toward the welding starting point 115a of the center shell 104a. Because the end shell 104b can shift freely in a radial direction in the center shell 104a at that stage, a gap can be formed between the end shell 104b and the center shell 104a at the location remote from the welding starting point 115a as shown in FIG. 20, thereby preventing welding from causing internal stress.
After that, the melted metal gradually solidifies along the route where the welding has progressed. As a result, portions of the center shell 104a are drawn toward the end shell 104b, and the center shell 104a is deformed in a way to collapse inwardly. How much the center shell 104a is deformed inwardly is roughly proportional to the size of the gap between the end shell 104b and the center shell 104a. It means that the deformation at the side of the center shell 104a remote from the welding starting point 115a, i.e. the deformation in the direction of a welding point 114a of the arc spot welding is the greatest. Since the subframe 104b also slightly shifts toward the welding starting point 115a, in addition to such deformation as indicated by an arrow in FIG. 21, coaxiality of the subframe 104b with respect to the frame 103 deteriorates. It creates a problem in that if this deterioration exceeds an acceptable limit, the rotation of the main shaft 109 supported by the bearings 103c and 108a becomes worse to damage performance.
It is a second object of the present invention to solve this problem, and to provide a scroll type compressor capable of make the rotation of a main shaft smooth and of preventing performance from being damaged without deteriorating coaxiality of a subframe with respect to a frame by subjecting an end shell to welding.